The long term goal of this program is to derive a better understanding of the mechanisms of the regulation of gene expression at the eukaryotic level of cellular and genetic organization. The biochemical, genetic, and physiological aspects of the mechanisms of the induction and metabolic regulation of the galactose utilizing enzymes (Leloir enzymes) in the yeast Saccharomyces cerevisiae will be studied as a model system of regulation in eukaryotic cells. This program is a continuation of and expansion of current program with a greater emphasis on the utilization of genetic and biochemical techniques. The following areas will be investigated: using whole cells permeabilized with DMSO, the coordinancy of the induction of the Leloir enzymes will be determined; the effects of different metabolic parameters on the expression of the Leloir enzymes in wild type and mutant strains will be studied using both batch and chemostat culture techniques; the observed differential effect of glucose on different regulatory mutants of the system will be studied in order to elucidate the molecular mechanism of catabolite repression of the system; the biochemical basis of long-term adaptation mutants of yeast will be analysed by biochemical techniques; the molecular function of the Gal 4 gene cytoplasmic product will be investigated using temperature- sensitive mutants; the relationship between aerobic respiration and enzyme synthesis will be clarified in both respiratory-competent and incompetent strains; a novel mutation conferring resistance to metabolic toxicity by Leloir pathway intermediates will be genetically and biochemically characterized. Data obtained will be correlated with data obtained from the study of prokaryotic catabolic systems and other fungal systems and related to the metabolism of galactose in normal and galactosemic persons.